This invention relates to electrostatic transducers and more particularly to brushless printed circuit angle resolvers incorporating capacitive coupling techniques.
A number of prior art angle resolvers incorporate electrostatic coupling techniques to produce a signal indicative of angular position. One type of angle resolver is an electrostatic position transducer having the desirable features of flexibility in design configuration and low cost. The electrostatic angle resolver is essentially comprised of two variably shaped metallic plates rotated in opposition to each other to vary the plate surface area exposed between the two plates thereby creating a variable electrostatic field signal. The electrostatic charge acquired by the moving plate is reflected back to a stationary coupling or receiving plate and transformed into an electronic signal which, when analyzed reveals angular position or variations in angular position. Examples of such devices are shown in U.S. Pat. No. 4,092,579 to Wheit, U.S. Pat. No. 4,040,041 to Fletcher et al., U.S. Pat. No. 4,435,702 to Imai, U.S. Pat. No. 3,961,318 to Farrand et al., U.S. Pat. No. 4,418,348 to Tanaka et al., and U.S. Pat. No. 4,238,781 to Vercellotti et al.
Each of the devices disclosed in the above patents relies upon some form of external excitation. Additionally, it is likely in many applications that these devices will be used in and about metallic objects. As the rotor or stator become more closely located to a nearby metallic object, the quality or strength of the signal which is reflected from the rotor to the stator can be diminished due to the nearby grounded metallic object. Thus, a primary difficulty with the prior art in terms of location of an angle resolver depends upon the application site and nearby metallic objects. In order to avoid the interference caused by nearby metallic objects, the present invention includes a device for shielding the stator and rotor from nearby interferences so as to provide a higher quality signal and thus an improved signal for sensing angular position. By providing such shielding concepts, the present invention enables flexibility in the packaging of the angular resolver for each particular application, regardless of the proximity of metallic objects.